Shareholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Interest-rate contracts, net of related taxes of $0 and $2, respectively	$ 2,084	$ 2,088	$ 2,260
Sales of non-U.S. entities, net of related taxes of ($2) and $0, respectively	(372)	(735)	$ (889)
Total reclassifications into AOCI	(9)	77
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gains (Losses) on Cash Flow Hedges | Interest-rate contracts
Class of Stock [Line Items]
Interest-rate contracts, net of related taxes of $0 and $2, respectively	0	(3)
Interest-rate contracts, taxes	0	2
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gains (Losses) on Available-for-Sale Securities
Class of Stock [Line Items]
Net realized gains from sales of available-for-sale securities, net of related taxes of ($4) and $1, respectively	6	(6)
Net realized gains from sales of available-for-sale securities, taxes	(4)	(1)
Reclassification out of Accumulated Other Comprehensive Income | Other-Than-Temporary Impairment on Securities
Class of Stock [Line Items]
Other-than-temporary impairment on held-to-maturity securities related to factors other than credit, net of related taxes of $1 and $0, respectively	(1)	(2)
Other-than-temporary impairment on held-to-maturity securities related to factors other than credit, taxes	1	0
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Actuarial Losses
Class of Stock [Line Items]
Amortization of actuarial losses, net of related taxes of ($1) and ($51), respectively	(11)	88
Amortization of actuarial losses, taxes	(1)	(51)
Reclassification out of Accumulated Other Comprehensive Income | Foreign Currency Translation
Class of Stock [Line Items]
Sales of non-U.S. entities, net of related taxes of ($2) and $0, respectively	(3)	0
Sale of non-U.S. entities, taxes	$ (2)	$ 0